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Phytosterols are
phytosteroid Phytosteroids, also known as plant steroids, are naturally occurring steroids that are found in plants. Examples include digoxin, digitoxin, diosgenin, and guggulsterone, as well as phytosterols like β-sitosterol and other phytoestrogens A phy ...
s, similar to
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
, that serve as structural components of biological membranes of
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s. They encompass plant
sterol Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the go ...
s and stanols. More than 250 sterols and related compounds have been identified. Free phytosterols extracted from oils are insoluble in water, relatively insoluble in oil, and soluble in alcohols. Phytosterol-enriched foods and
dietary supplement A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources or that are synthetic in order ...
s have been marketed for decades. Despite well-documented
LDL cholesterol Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densit ...
-lowering effects from long-term consumption of phytosterols, there is insufficient evidence for an effect on
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...
s,
fasting blood sugar Many types of glucose tests exist and they can be used to estimate blood sugar levels at a given time or, over a longer period of time, to obtain average levels or to see how fast body is able to normalize changed glucose levels. Eating food for e ...
,
glycated hemoglobin Glycated hemoglobin, also known as HbA1c, glycohemoglobin, hemoglobin A1c, A1C, is a form of hemoglobin (Hb) that is chemically linked to a sugar. Most monosaccharides, including glucose, galactose and fructose, spontaneously (i.e. non-enzymatic ...
, or overall
mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of de ...
.


Structure

They have a fused polycyclic structure and vary in carbon side chains and / or presence or absence of a
double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
(saturation). They are divided into 4,4-dimethyl phytosterols, 4-monomethyl phytosterols, and 4-desmethyl phytosterols based on the location of methyl groups at the carbon-4 position. Stanols are
saturated Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds ** Saturated and unsaturated compounds **Degree of unsaturation ** Saturated fat or fatty ac ...
sterols, having no double bonds in the sterol ring structure. The molecule in the article lead is
β-sitosterol β-sitosterol (beta-sitosterol) is one of several phytosterols (plant sterols) with chemical structures similar to that of cholesterol. It is a white, waxy powder with a characteristic odor, and is one of the components of the food additive E499. ...
. The nomenclature is shown on the right. *By removing carbon 242,
campesterol Campesterol is a phytosterol whose chemical structure is similar to that of cholesterol, and is one of the ingredients for E number E499. Natural occurrences Many vegetables, fruits, nuts, and seeds contain campesterol, but in low concentratio ...
is obtained. *By removing carbons 241 and 242,
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
is obtained. *Removing a hydrogen from carbons 22 and 23 yields
stigmasterol Stigmasterol – a plant sterol (''phytosterol'') – is among the most abundant of plant sterols, having a major function to maintain the structure and physiology of cell membranes. In the European Union, it is a food additive listed with E numb ...
(stigmasta-5,22-dien-3β-ol). *By hydrogenating the double bond between carbons 5 and 6, β- sitostanol (Stigmastanol) is obtained. *By hydrogenating the double bond between carbons 5 and 6 and removing carbon 242,
campestanol Campestanol is a natural phytosterol Phytosterols are phytosteroids, similar to cholesterol, that serve as structural components of biological membranes of plants. They encompass plant sterols and stanols. More than 250 sterols and related com ...
is obtained. *Removing carbon 242 and hydrogens from carbons 22 and 23, and inverting the stereochemistry at C-24 yields brassicasterol (ergosta-5,22-dien-3β-ol). *Further removal of hydrogens from carbons 7 and 8 from brassicasterol yields
ergosterol Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol found in cell membranes of fungi and protozoa, serving many of the same functions that cholesterol serves in animal cells. Because many fungi and protozoa cannot survive without ergosterol, the ...
(ergosta-5,7,22-trien-3β-ol). Important: Ergosterol is not a plant sterol. Ergosterol is a component of fungal cell membranes, serving the same function in fungi that cholesterol serves in animal cells. In addition: *Esterification of the hydroxyl group at carbon 3 with fatty/organic acids or carbohydrates results in plant
sterol ester Sterol esters are a heterogeneous group of chemical compounds. They are created when the hydroxyl group of a sterol and a fatty acid undergo an esterification reaction. They can be found in trace amounts in every cell type but are highly enriched i ...
s, i.e. oleates, ferulates and (acyl) glycosides. File:Sitosterol structure.svg,
β-sitosterol β-sitosterol (beta-sitosterol) is one of several phytosterols (plant sterols) with chemical structures similar to that of cholesterol. It is a white, waxy powder with a characteristic odor, and is one of the components of the food additive E499. ...
File:campesterol.svg,
Campesterol Campesterol is a phytosterol whose chemical structure is similar to that of cholesterol, and is one of the ingredients for E number E499. Natural occurrences Many vegetables, fruits, nuts, and seeds contain campesterol, but in low concentratio ...
File:Stigmasterin.svg,
Stigmasterol Stigmasterol – a plant sterol (''phytosterol'') – is among the most abundant of plant sterols, having a major function to maintain the structure and physiology of cell membranes. In the European Union, it is a food additive listed with E numb ...
File:Stigmastanol.svg, Stigmastanol File:campestanol.svg,
Campestanol Campestanol is a natural phytosterol Phytosterols are phytosteroids, similar to cholesterol, that serve as structural components of biological membranes of plants. They encompass plant sterols and stanols. More than 250 sterols and related com ...
File:brassicasterol.svg, Brassicasterol File:Cycloartenol.svg,
Cycloartenol Cycloartenol is an important triterpenoid of the sterol class which is found in plants. It is the starting point for the synthesis of almost all plant steroids, making them chemically distinct from the steroids of fungi and animals, which are, ins ...
 File:cholesterol.svg,
Cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
Image:ergosterol.svg,
Ergosterol Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol found in cell membranes of fungi and protozoa, serving many of the same functions that cholesterol serves in animal cells. Because many fungi and protozoa cannot survive without ergosterol, the ...


Dietary phytosterols

The richest naturally occurring sources of phytosterols are vegetable oils and products made from them. Sterols can be present in the free form and as
fatty acid ester Fatty acid esters (FAEs) are a type of ester that result from the combination of a fatty acid with an alcohol. When the alcohol component is glycerol, the fatty acid esters produced can be monoglycerides, diglycerides, or triglycerides. Dietary f ...
s and
glycolipids Glycolipids are lipids with a carbohydrate attached by a glycosidic (covalent) bond. Their role is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the connec ...
. The bound form is usually hydrolyzed in the small intestines by pancreatic enzymes. Some of the sterols are removed during the deodorization step of refining oils and fats, without, however, changing their relative composition. Sterols are therefore a useful tool in checking authenticity. As common sources of phytosterols,
vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fat ...
s have been developed as
margarine Margarine (, also , ) is a spread used for flavoring, baking, and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The spread was orig ...
products highlighting phytosterol content. Cereal products, vegetables, fruit and berries, which are not as rich in phytosterols, may also be significant sources of phytosterols due to their higher intakes. The intake of naturally occurring phytosterols ranges between ~200–300 mg/day depending on eating habits. Specially designed vegetarian experimental diets have been produced yielding upwards of 700 mg/day. The most commonly occurring phytosterols in the human diet are β-sitosterol, campesterol and stigmasterol, which account for about 65%, 30% and 3% of diet contents, respectively. The most common plant ''stanols'' in the human diet are sitostanol and campestanol, which combined make up about 5% of dietary phytosterol.


Health claims


EFSA

The European Foods Safety Authority (EFSA) concluded that
blood cholesterol Blood lipids (or blood fats) are lipids in the blood, either free or bound to other molecules. They are mostly transported in a protein capsule, and the density of the lipids and type of protein determines the fate of the particle and its influence ...
can be reduced on average by 7 to 10.5% if a person consumes 1.5 to 2.4 grams of plant sterols and stanols per day, an effect usually established within 2–3 weeks. Longer-term studies extending up to 85 weeks showed that the cholesterol-lowering effect could be sustained. Based on this and other efficacy data, the EFSA scientific panel provided the following health advisory: "Plant sterols have been shown to lower/reduce blood cholesterol. Blood cholesterol lowering may reduce the risk of
coronary heart disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...
".


FDA

The
FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
has approved the following claim for phytosterols: ''For plant
sterol ester Sterol esters are a heterogeneous group of chemical compounds. They are created when the hydroxyl group of a sterol and a fatty acid undergo an esterification reaction. They can be found in trace amounts in every cell type but are highly enriched i ...
s'': (i) Foods containing at least 0.65 g per serving of plant sterol esters, eaten twice a day with meals for a daily total intake of at least 1.3 g, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of
ame of the food #REDIRECT AME #REDIRECT AME {{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...
{{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...
supplies ___grams of vegetable oil sterol esters. ''For plant stanol esters'': (i) Foods containing at least 1.7 g per serving of plant stanol esters, eaten twice a day with meals for a total daily intake of at least 3.4 g, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of
ame of the food #REDIRECT AME #REDIRECT AME {{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...
{{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...
supplies ___grams of plant stanol esters. Reviewing clinical trials involving phytosterol supplementation, the FDA concluded that when consumed in the range of 1 to 3 grams in enriched foods, phytosterols resulted in statistically significant (5-15%) reductions in blood LDL cholesterol levels relative to placebo. The FDA also concluded that a daily dietary intake of 2 grams a day of phytosterols (expressed as non-esterified phytosterols) is required to demonstrate a relationship between phytosterol consumption and cholesterol lowering for reduced CVD risk.


Health Canada

Health Canada Health Canada (HC; french: Santé Canada, SC)Health Canada is the applied title under the Federal Identity Program; the legal title is Department of Health (). is the Structure of the Canadian federal government#Departments, with subsidiary unit ...
reviewed the evidence of 84 randomized controlled trials published between 1994 and 2007 involving phytosterol supplementation. An average 8.8% reduction in LDL-cholesterol was observed at a mean intake of 2 grams per day. Health Canada concluded that sufficient scientific evidence exists to support a relationship between phytosterol consumption and blood cholesterol lowering. Based on this evidence, Health Canada approved the following statements for qualifying foods intended for hypercholesterolemic individuals: Primary statement: "
erving size from Nutrition Facts table in metric and common household measures Erving may refer to: People * Cameron Erving (born 1992), American college football player * George W. Erving (1769–1850), American diplomat * Julius Erving (born 1950), American basketball player, also known as "Dr. J" * Erving Goffman (1922 ...
of
aming the product Aming (あみん) is female Japanese pop/folk duo composed of Takako Okamura and Haruko Kato that debuted in 1982 with their hit "Matsu wa is the debut single by Aming released on July 21, 1982 in Japan. Track list # "Matsu wa" (待つわ) ...
provides X% of the daily amount* of plant sterols shown to help reduce/lower cholesterol in adults." Two additional statements that could be used in combination or alone, adjacent to the primary statement, without any intervening printed, written or graphic material: "Plant sterols help reduce
r help lower R, or r, is the eighteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ar'' (pronounced ), plural ''ars'', or in Irelan ...
cholesterol." This statement when used, shall be shown in letters up to twice the size and prominence as those of the primary statement. "High cholesterol is a risk factor for heart disease." This statement when used, shall be shown in letters up to the same size and prominence as those of the primary statement.


Cholesterol lowering

The ability of phytosterols to reduce
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
levels was first demonstrated in humans in 1953. From 1954 to 1982, phytosterols were subsequently marketed as a pharmaceutical under the name Cytellin as a treatment for elevated cholesterol. Unlike the
statin Statins, also known as HMG-CoA reductase inhibitors, are a class of lipid-lowering medications that reduce illness and mortality in those who are at high risk of cardiovascular disease. They are the most common cholesterol-lowering drugs. Low- ...
s, where cholesterol lowering has been proven to reduce risk of
cardiovascular diseases Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, ...
(CVD) and overall mortality under well-defined circumstances, the evidence has been inconsistent for phytosterol-enriched foods or supplements to lower risk of CVD, with two reviews indicating no or marginal effect, and another review showing evidence for use of dietary phytosterols to attain a cholesterol-lowering effect. Coadministration of statins with phytosterol-enriched foods increases the cholesterol-lowering effect of phytosterols, again without any proof of clinical benefit and with anecdotal evidence of potential
adverse effects An adverse effect is an undesired harmful effect resulting from a medication or other intervention, such as surgery. An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. The term complica ...
. Statins work by reducing cholesterol synthesis via inhibition of the rate-limiting
HMG-CoA reductase HMG-CoA reductase (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, official symbol HMGCR) is the rate-controlling enzyme (NADH-dependent, ; NADPH-dependent, ) of the mevalonate pathway, the metabolic pathway that produces cholesterol and oth ...
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
. Phytosterols reduce cholesterol levels by competing with cholesterol absorption in the gut via one or several possible mechanisms, an effect that complements statins. Phytosterols further reduce cholesterol levels by about 9% to 17% in statin users. The type or dose of statin does not appear to affect the cholesterol-lowering efficacy of phytosterols. Because of their cholesterol reducing properties, some manufacturers are using sterols or stanols as a food additive.


Safety

Phytosterols have a long history of safe use, dating back to Cytellin, the pharmaceutical preparation of phytosterols marketed in the US from 1954 to 1982. Phytosterol esters have generally recognized as safe (GRAS) status in the US. Phytosterol-containing
functional food A functional food is a food claimed to have an additional (often one related to health promotion or disease prevention) by adding new ingredients or more of existing ingredients. The term may also apply to traits purposely bred into existing edi ...
s were subject to postlaunch monitoring after being introduced to the EU market in 2000, and no unpredicted side effects were reported. A potential safety concern regarding phytosterol consumption is in patients with phytosterolaemia, a rare genetic disorder which results in a 50- to 100-fold increase in blood plant sterol levels and is associated with rapid development of coronary atherosclerosis. Phytosterolaemia has been linked to mutations in the ABCG5/G8 proteins which pump plant sterols out of enterocytes and hepatocytes into the lumen and bile ducts, respectively. Plant sterol levels in the blood have been shown to be positively, negatively or not associated with CVD risk, depending on the study population investigated. The link between plant sterols and CVD or CHD risk is complicated because phytosterol levels reflect cholesterol absorption. (See Phytosterols as a marker for cholesterol absorption).


Sterol vs stanol

The equivalent ability and safety of plant sterols and plant
stanol Stanol esters is a heterogeneous group of chemical compounds known to reduce the level of low-density lipoprotein (LDL) cholesterol in blood when ingested, though to a much lesser degree than prescription drugs such as statins. The starting materi ...
s to lower cholesterol continues to be a hotly debated topic. Plant sterols and stanols, when compared head-to-head in clinical trials, have been shown to equally reduce cholesterol levels. A meta-analysis of 14 randomized, controlled trials comparing plant sterols to plant stanols directly at doses of 0.6 to 2.5 g/day showed no difference between the two forms on total cholesterol, LDL cholesterol, HDL cholesterol, or triglyceride levels. Trials looking at high doses (> 4 g/day) of plant sterols or stanols are very limited, and none have yet to be completed comparing the same high dose of plant sterol to plant stanol. The debate regarding sterol vs. stanol safety is centered on their differing intestinal absorption and resulting plasma concentrations. Phytostanols have a lower estimated intestinal absorption rate (0.02 - 0.3%) than phytosterols (0.4 - 5%) and consequently blood phytostanol concentration is generally lower than phytosterol concentration.


Research

Phytosterols are under preliminary research for their potential to inhibit lung, stomach, ovarian and breast cancers, as well as colon and prostate cancers.


Functions in plants

Sterols are essential for all
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s. In contrast to animal and
fungal A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...
cells, which contain only one major sterol, plant cells synthesize an array of sterol mixtures in which
sitosterol β-sitosterol (beta-sitosterol) is one of several phytosterols (plant sterols) with chemical structures similar to that of cholesterol. It is a white, waxy powder with a characteristic odor, and is one of the components of the food additive E499. ...
and
stigmasterol Stigmasterol – a plant sterol (''phytosterol'') – is among the most abundant of plant sterols, having a major function to maintain the structure and physiology of cell membranes. In the European Union, it is a food additive listed with E numb ...
predominate. Sitosterol regulates membrane fluidity and permeability in a similar manner to cholesterol in mammalian cell membranes. Plant sterols can also modulate the activity of membrane-bound enzymes. Phytosterols are also linked to plant adaptation to temperature and plant immunity against pathogens.


References

{{Cholesterol metabolism intermediates Food additives Hypolipidemic agents